This invention relates to railroads, particularly to methods of sorting cars in railroad yards.
Copending utility patent application Priority Car Soiling In Railroad Classification Yards Using a Continuous Multi-Stage Method by Edwin R. Kraft, Ser. No. 09/716,300 (hereinafter referred to as the xe2x80x9cparent applicationxe2x80x9d) describes new methods of multiple stage sorting in railroad classification yards. It also suggests several new yard designs to maximize the effectiveness of those methods. An extensive review of prior art is also included in the parent application. Further refinements to those operating methods and yard designs are disclosed herein.
Copending U.S. application Ser. No. 09/716,300 is incorporated by reference into this application, as provided by Manual of Patent Examining Procedure, Section 608.01(p). However, some repetition of material already covered in the parent application is necessary. In cases where drawing figures or tables from the parent application are referenced, they keep their same figure numbers (1-22), labels and reference numbers herein. Therefore, any repetitive material which does need to be included herein can easily be identified and cross referenced with the parent application.
Prior art designs for large railway classification yards dedicate specific tracks to distinct functions of receiving inbound trains, classification (sorting) of cars, and to assembly of outbound trains. Cars always move in a predetermined sequence from the receiving yard through the classification yard, and finally into the departure yard. Hump yards are modeled after an assembly line. The problem is that it is a rigid Henry Ford, 1920""s-style assembly line, rather than adapting yard design to current just-in-time manufacturing paradigmsxe2x80x94which emphasize flexibility, short setup times and rapid response to changing and always unpredictable customer needs. This lack of flexibility inherent in current yard designs translates into an inability to:
(a) make connections as scheduled,
(b) protect capacity on outbound trains needed for higher priority cars,
(c) accommodate xe2x80x9cblock swappingxe2x80x9d or
(d) benefit from switching already done at a previous yard.
Accordingly, major changes in design philosophy are needed to make hump yards effective in today""s truck-competitive environment. Currently, hump yards generally use single stage sorting, where each car is classified only once. Single stage sorting is very restrictive, since it limits the number of classifications or xe2x80x9cblocksxe2x80x9d that can be built to no more than the number of tracks in the yard, and once cars are classified, affords no xe2x80x9csecond chancexe2x80x9d to adjust the arrangement of cars. Even if a yard is built with many short tracks, single stage yards often cannot create as many blocks as are needed. Since classification tracks are usually too short to assemble outbound trains, cars have to be pulled out of the opposite end of the yard, called the xe2x80x9ctrimxe2x80x9d end and moved into a separate departure yard having longer tracks. Usually this xe2x80x9cflatxe2x80x9d switching operation, and not the sorting capacity of the hump, limits maximum throughput of the yard.
In a multiple stage yard, each car may be classified more than once allowing cars to be sorted into many more blocks (distinct classifications) than the number of tracks available. As shown in the parent application if classification tracks are of sufficient length, trains of more than one block can be built xe2x80x9cready to goxe2x80x9d on a single track in proper order for departure, without needing flat switching at the trim end of the yard. The second sorting stage at the hump replaces flat switching for outbound train assembly, resulting in no net increase in switching workload.
Having eliminated the flat switching bottleneck at the xe2x80x9ctrimxe2x80x9d end of the yard, the capacity of a multiple stage yard is clearly constrained by the hump processing rate. A high processing rate is needed since each car must be classified two or three times in a multiple stage yard, as compared to only once in a single stage yard. This need for high capacity has been recognized for a long time, in fact, a lack of sufficient capacity using traditional gravity sorting has been thought to render multiple stage switching infeasible. In The Folded Two Stage Railway Classification Yard, (hereinafter referred to as Davis, 1967) on p. 55 the two-fold yard was characterized as xe2x80x9ca new concept in yard design. It may never have been proposed before because it would be inoperative using the sorting techniques presently employed by railroads. The yard uses neither an engine nor gravity to separate the cars.xe2x80x9d Instead, Davis proposed use of a mechanical car accelerator to boost sorting capacity.
Although some U.S. yards have classified over 3,000 cars per day across a single gravity hump, with the increasing weight and length of modern cars, yard capacity has been slowly reduced. A typical hump yard today classifies 2,000-2,500 cars per day. A multiple stage yard of the same capacity would need a humping capability of 5,000-7,500 cars per day. This invention shows how the capacity needed to enable practical multiple stage sorting can be attained within the proven capability of conventional gravity switching, without needing to resort to any exotic or untested mechanical devices for accelerating or controlling the speed of railcars.
Shortcomings of Previous Designs
FIG. 10 of the parent application shows a design for a multiple stage classification yard. This yard consists of a single body of long classification tracks 55, which should have a slight descending gradient throughout their entire length, so cars will roll all the way to the ends of the tracks. With such a gradient, car speed can be adequately controlled using only retarder units, avoiding the necessity for more expensive booster units. FIG. 22 of the parent application shows how xe2x80x9cDowtyxe2x80x9d car retarders may be distributed throughout the entire length of each track to maintain continuous speed control of cars, and to stop the cars upon reaching the end of each track.
The design of FIG. 10 of the parent application permits maximum flexibility in use of classification tracks for receiving inbound trains, sorting of cars and for final assembly of outbound trains. Cart roads 60 between every pair of tracks allow convenient access by mechanical personnel for performing car inspection and repairs, and for maintaining tracks, switches and car retarder systems.
Means for accelerating cars 90 into the classification tracks (generally assumed to be a gravity hump) are provided at one end of the yard. Switches at the opposite end of the yard, called the arrival/departure end 80, allow trains to arrive and depart the yard onto the mainline 30 without interfering with hump 90 activities. Flat switching can also be performed at the arrival/departure end 80, permitting xe2x80x9cswappingxe2x80x9d blocks of preclassified cars directly from one train to another, avoiding the need for those cars to be processed over the hump.
The main weakness of the yard shown in FIG. 10 of the parent application is that it only allows one train to be processed at a time. This severely constrains its capacity. FIGS. 14 and 15, also from the parent application, suggest placing a hump on both ends of the yard to increase its sorting capacity. However, such xe2x80x9cdouble endedxe2x80x9d designs can be problematical for the following reasons:
(a) It becomes necessary to coordinate processing activities of two humps at both ends of the yard, since cars cannot be safely humped into a track from both directions simultaneously.
(b) Double ended designs cause difficulties in establishing proper gradients throughout the length of the yard. Cars would tend to collect at the low point of the yard in the middle, rather than rolling all the way to the ends of the tracks. This problem could be overcome, at some cost, by employing booster units (an optional feature of the xe2x80x9cDowtyxe2x80x9d retarder system) to keep the cars rolling.
(c) Humps 90a and 90b on both ends of the yard block access to classification tracks 55 needed by arriving and departing trains, and also prevent flat switching. Although the lapped design as in FIG. 15 of the parent application partially addresses the problem, a fully open arrival/departure end 80 as shown in FIG. 10 of the parent application is even more desirable to minimize interference with hump 90 operations.
(d) Finally, sorting activity in a double-ended yard may become so intense as to render impractical the inspection and repair of cars while they lie in the classification tracks. This defeats one of the main benefits of multiple stage switching, which is the ability to effectively utilize car time waiting for connections to perform maintenance and other mechanical servicing activities.
The high capacity multiple-stage yard of FIG. 1, which consists of two subyards, does not suffer the limitations associated with a double ended design. Each subyard has a fully open arrival/departure end, and may have a continuously descending gradient throughout the entire length of its classification tracks. The design of FIG. 10 in the parent application which is used as a template, can be replicated as many times as needed to attain the needed total capacity. The key to success of this design is positioning the subyards opposite one another, so classification tracks of one subyard can serve as receiving tracks for the other subyard. By interconnecting the escape tracks 10 between the two yards as shown in FIG. 1, the facility not only has higher capacity but even more efficiency and flexibility than a single yard by itself.
A very simple, but critical improvement shown in both FIGS. 1 and 3 is provision of a double hump lead track 40. By providing scizzors crossovers 140 at the hump crest, any classification track 55 can be reached from either hump lead track 40. (These are labeled 40a, 40b, 55a, 55b, 140a and 140b in FIG. 1 because those features are replicated in both subyards.) Although double hump leads with crossovers are often provided in single stage yards, they are of limited value since parallel hump operations frequently interfere with one another. In a single stage yard a second hump lead can be used to preposition trains for processing, but seldom can two humping operations proceed at once. But in a multiple stage yard during second stage sorting, cars are sorted into just a few tracks representing the outbound train(s) currently being assembled. If all these tracks are located on the same side of the yard, two hump operations can proceed concurrently without interference.
Since over half the hump processing time in a multiple stage yard is consumed by second stage sorting, dual hump leads can be of considerable value. In a multiple stage yard, dual leads are much more useful than in traditional single stage yards, since they can boost capacity by at least 50%.
By providing two subyards as shown in FIG. 1, capacity is further doubled, since operations in the two subyards do not interfere with one another. By providing four hump switching leads (as compared to only a single lead in the yard of FIG. 10 in the parent application) hump capacity is increased by a factor of at least three times. By comparison, using the triangular sorting pattern, each car must be sorted on the average between 2.5 and 3 times. Therefore, it should be apparent that the capacity of the yard of FIG. 1 will be comparable to that of a large conventional single stage yard. This is accomplished without requiring inordinately high hump processing rates or any unusual mechanical means for accelerating or regulating the speed of cars. This capacity is achievable using conventional, proven gravity switching methods, and assumes that each car will have to be classified up to three times before it finally departs the yard.
The preceding discussion shows how the required capacity increase can be achieved through physical design of the yard facility. However, capacity can be further increased and costs reduced even more by utilizing the special yard operating methods proposed here. The first method exploits specific features of the track configuration shown in FIG. 1. The second method relies on a system of partial preclassification of cars to eliminate the need for first stage sorting, which by itself can almost double yard capacity. That method can be utilized in the yard of FIG. 10 in the parent application as well. Each of these operating methods are detailed in the following sections.
Objects and Advantages
Several objects and advantages of the present invention are:
(a) As shown in FIG. 3, capacity can be increased by providing a double hump lead with scizzors crossovers instead of only a single switching lead across the hump. Using this second hump lead during second stage switching operations can boost capacity by at least 50%.
(b) By positioning two or more subyards opposite one another, interconnecting the escape tracks and providing crossover tracks in the classification yard as in FIG. 1, one subyard can receive trains for processing in the opposite subyard. This eliminates the need for one xe2x80x9cpull backxe2x80x9d move. With two subyards, operation as a xe2x80x9cfoldedxe2x80x9d yard also becomes possible. Provision of a second subyard (where each subyard has a double hump lead with scizzors crossovers) increases capacity by at least three times, as compared to the yard shown in FIG. 10 of the parent application.
(c) Cars can be partially preblocked at preceding yards to bypass the first stage sort. By enabling better utilization of the double hump lead as well as directly reducing the number of cars that have to be switched, partial preblocking can more than double the capacity of the yard. Implementing all three improvements at once, the capacity of the yard of FIG. 10 in the parent application can be increased by a factor of at least six times.
Still further objects and advantages will become apparent from consideration of the ensuing description and drawings.